Upload sometimes hangs

we normally do not have any issue uploading files but, sometimes, instead of the normal 2,3 seconds needed to upload, it take 5…10…15 seconds: then the upload process is over, but nothing is actually uploaded.

Any advice? (even on how to debug?)

Suitecrm **Version 7.11.18**
O.s.: Centos 7.9.200 (updated)
PHP 7.3.27

You can check your logs:

Take a look into this post for information on logs: